Method of treating molten magnesium and its high-percentage alloys



Patented'jam 6, 1931 ADOLF BECK, WALTHER' SCHMIDT, AND

GUSTAV sbHREIBER, or BITTERFELD, elix- MANY, ASSIGNOIRS TO I. G. FARBENINDUSTBIE AK'I'IENGESELLSCHAFT, OF FRANK- FORT-ON-THE-MAIN, GERMANY, A CORPORATION OF GERMANY METHOD OF TREATING MOLTEN MAGNESIUM AND ITS HIGH-PERCENTAGE ALLOYS Application filed August 20, 1928, Serial No. 300,840, and in Germany March 4, 1927.

' This invention relates to the treatment of magnesium and its high-percentage alloys in the molten state. I It is well known that the air-exposed surfaces of molten easily oxidizable metals such as magnesium and its high-percentage alloys readily form films of a generally exceedingly tenuous though sometimes decidedly tough structure by reaction with the atmosphere. It is hardly possible to determine the composition of these films accurately; it may be supposed that they chiefly consist of oxide and nitride compounds of the various constituents of the alloys, though-we do not wish to limit ourselves by this explanation, the expression reaction covering effects produced by chemical as well as physical processes. These'films are also formed whenever a free jet of molten metal is exposed to the atmosphere, for instance, in pouring the metal from ladles or melting pots into molds. Although these layers'a're in such cases hardly visible, they are notwithstanding of noticeable influence in foundry practice since they are apt to tear up during the casting operation, the bits of the layer are swept into'the mold, and every particle of these films occluded. by the casting interrupts the continuity of its inter-.

crystalline structure thus impairing the soundness of the roduct. Another difficulty arises from the ot that particles of fluxes or other foreign substances floating on the surface of the molten metal in the pot, fretothese films and are thus swept into the moulds formquently adhere also frequently ing inclusions in the castings of a decidedly undesirable nature.

The present invention is based on the observation that, during this film also rapidly of the metal coming This applies not only casting pool, but more particularly also to the jet of flowing metal. We have. discovered forms on every surface lIltO contact with air.

a that by a particular method of pouring the metal, this film, once it is formed, can be held in a stationary position, form-in a kind of hose through which the metal ows as The reaction products constituting the hose are thus efficiently the pouring operation,

to the surface of the prevented from entering the mold as long as the hose is kept intact, and at the same time the flowing metal itself is protected from further oxidation by the hose which is practically impermeable to the reactive constituents of the air. Thus a continuous coherent film is formed covering the surface of the metal in the pot as well as the jet of flowing v drawn into the casting. v

raised simultaneously. Any sudden mov'ement, however, particularly a raising, of the the pot should carefully be avoided, because the protective film becomes easily, roverstrained and is then severed and its pieces v swept into the mould. It is rather preferl able to effect the tipping of the crucible by using its mouth as a pivot point so as to keep a fixeddistance between the mould and the mouth of the pot during the whole pouring. procedure. By this means it is possible to prevent the film from being severed and moving along with th'emetal into the mould. Particles of fluxes or slag floating on the surface of the metal in the pot are embedded in this film and therefore cannot be swept into the mould as long as the film of reaction roducts remains in its position on the suriiioe of the metal.

When the mould is filled completely the crucible is taken away, thus separating it from the hose which now falls down on the casting pool without afiecting the casting itself.

, The annexed 'drawin gives a diagram-'- matic view of the conditions prevailing during the casting operation according to our invention. The crucible which it will be noticed is tipped, with the mouth being the pivot point is reproduced in two positions cor- 1' the sand mould wit more favourably influenced by adding to the ceiving mold atmosphere surrounding the flowing metal and the molten metal in the ladle or crucible substances capable of forming reaction products with the metal suitable to reinforce the structure of the film forming the hose. To this effect We prefer to spray finely divided sulphur over the jet'ot metal during the pouring operation.

The number and the shape of the gates of" the mould is to be calculated in accordance with the above-described method; to this end it will often be necessary, in the case 0 larger castings, to cast from several small crucibles instead from a large one, it when using the latter the conditions for preserving the hose cannot be fulfilled.

We claim:

1. A method of protecting a jet of molten magnesium and high-percentage magnesium alloys from oxidation, comprising the step of keeping the point of issue of the metal from the pouring vessel in a substantially fixed position relative to the gate of the re ceiving mold whereby the jet of metal between the pouring vessel and the receiving mold in contact with the air forms a rigid hose through which theremainder of the metal in the pouring vessel can flow without contact with the air.

2. A method of protecting a jet of molten magnesium and high-percentage magnesium alloys from oxidation, comprising the step of keeping the point of issue of the metal from the pouring vessel in a substantially fixed position relative to the gate of the receiving mold, and maintaining a substantially constant rate of flow of the metal by steadily tilting the pouring vessel whereby the jet of metal between the pouring vessel and the receiving mold in contact with the air forms a rigid hose through which the remainder of the metal in the pouring vessel can flow without contact with the air. I

3. A method of protecting a jet of molten magnesium and high-percentage magnesium alloys from oxidation, comprising the step of keeping the point of issue of'the metal from the pouring vessel in a substantially fixed position relative to the gate of the re and addingto the atmosphere surrounding the molten metal a substance capable of forming a coherent film on the molten metal.

4/ A method of protecting a jet of molten magnesium and high-percentage magnesium alloys from oxidation, comprising the step of keeping the point of issue of the 'metal from the pouring vessel in a substantially fixed position relative to the gate of the receiving mold andadding to the atmosphere surrounding the molten metal a substance capable of forming, in co-action with air, a coherent film on the molten metal.

5. A method of protecting a jet of molten magnesium and high-percentage magnesium alloys from oxidation, comprising the step of keeping the point of issue of the metal from the pouring vessel in: a substantially fixed position relative to the gate of the receiving mold and adding to the atmosphere surrounding the molten metal sulfur in a finely divided form. t

6. A method of protecting a jet of molten magnesium and high-percentage magnesium alloys from oxidation, comprising the step of keeping-the point ofi issue of the metal from the pouring vessel in a substantially fixed position relative to the gate of the re-.

ceiving mold and spraying sulfur in a finely divided form towards the surface of the molten metal.

In testimony whereof we have hereunto set our hands.

ADOLF BECK. WALTHER- SCHMIDT. GUSTAV SCHREIBER. 

